So, I assume that thrust is a Vector2 object? Though, if that’s the case, that first line should have Vector2(0,50), not Vector(0,50)
Anyway, assuming it’s a Vector2, then the call to .rotated is a method on the Vector2 object. So, you can see its docs by looking at the Vector2 object and finding the rotated method, here:
There, you will see that the method rotates the vector by the specified number of radians.
So, your code will take the original vector (50,0) and rotate it by 1 radian. That results in a new Vector2, which is then passed into the set_applied_force call.